Amnesia

A character suffering from amnesia cannot
remember things; his name, his skills, and his past are all equal
mysteries. He can build new memories, but any memories that existed
before he became an amnesiac are suppressed.

Worse, the amnesiac loses all class abilities,
feats, and skill ranks for as long as his amnesia lasts. He retains his
base attack bonus, base saving throw bonuses, combat maneuver bonus,
combat maneuver defense, total experience points, and hit dice (and hit
points), but everything else is gone until the amnesia is cured. If a
character gains a class level while suffering from amnesia, he may use
any abilities gained by that class level normally. If the class level he
gained was of a class he already possess levels in, he gains the
abilities of a 1st-level character of that class, even though he is
technically of a higher level in that class. If his amnesia is later
cured, he regains all the full abilities of this class, including those
gained from any levels taken while he was suffering from amnesia.